1 Centre for Ecology and Hydrology, Edinburgh Research Station, Midlothian, Scotland, United Kingdom 2 Finnish Meteorological Institute, Helsinki, Finland Annual methane emission from Finnish mires estimated from eddy covariance campaign measurements K. J. Hargreaves 1 , D. Fowler 1 , C. E. R. Pitcairn 1 , and M. Aurela 2 With 8 Figures Received September 17, 1999 Revised October 16, 2000 Summary Measurements of landscape-scale methane emission were made over an aapa mire near Kaamanen in Finnish Lapland (69  8 0 N, 27  16 0 E, 155 m ASL). Emissions were measured during the spring thaw, in summer and in autumn. No effect of water table position on CH 4 emission was found as the water table remained at or above the surface of the peat. Methane emission ¯uxes increased with surface temperature from which an activation energy of 99 kJ mol 1 was obtained. Annual emission from the site, modelled from temperature regression and short-term ¯ux measurements made in three separate years, was calculated to be 5.5  0.4 g CH 4 m 2 y 1 of which 0.6  0.1 g CH 4 m 2 y 1 (11%) was released during the spring thaw which lasted 20 to 30 days. The effect of global warming on the CH 4 budget of the site was estimated using the central scenario of the SILMU (Finnish Research Programme on Climate Change) model which predicts annual mean temperature increases of 1.2, 2.4 and 4.4  C in 2020, 2050 and 2100, respectively. Maximum enhancements in CH 4 emission due to warming were calculated to be 18, 40 and 84% for 2020, 2050 and 2100, respectively. Actual increases may be smaller because prediction of changes in water table are highly uncertain. 1. Introduction After carbon dioxide, methane (CH 4 ) is the most important greenhouse gas in the troposphere, (IPCC, 1996). Global annual emissions are vari- ously estimated to be 597 Tg (IPCC, 1996), 505 Tg (Houweling et al., 1999), 600 Tg (Lelieveld et al., 1998) or 575 Tg (Hein et al., 1997). The quantity believed to come from natural wetlands is also variable, with values of 145  30 Tg (Lelieveld et al., 1998) or 232  27 Tg (Hein et al., 1997) being recent conclusions. Methane production in these anaerobic soils is closely regulated by water table depth and soil tempera- ture (MacDonald et al., 1998) and is therefore expected to be strongly in¯uenced by climate change. Methane emissions from this source could increase as the climate warms, but the magnitude of the increase and consequent effects on global warming are poorly de®ned. Several micrometeorological measurement programmes (for example Edwards et al., 1994; Fan et al., 1992; Harriss et al., 1992) have described CH 4 emissions from north American mire systems, but until now we are aware of only one study (Friborg et al., 1997) which has described micrometeorological measurements from a Fen- noscandian site, and this was restricted to a few days. Measurements of methane exchange over undisturbed Finnish mires have usually been carried out using chamber methods (for example Nyka Ènen et al., 1998 and Saarnio et al., 1997). During winter, frozen wetlands probably con- tinue to produce CH 4 which is unable to escape to the atmosphere at signi®cant rates because of the Theor. Appl. Climatol. 70, 203±213 (2001)